Messier 108 or M108 (also designated NGC 3556) is a spiral galaxy in the constellation Ursa Major. It has an apparent visual magnitude of 10 and its angular diameter is 8x1 arc-minutes. M108 lies at an estimated distance of 45 million light years. The Equinox 2000 coordinates are RA= 11h 11.5m, Dec= +55° 40´ which makes M108 best seen during the spring. The Messier Spring Star Chart shows the position of all Messier objects visible during that season.

The image above shows the uncropped view of galaxy M108 and planetary nebula M97 through the Takahashi E-180 Astrograph (North is up). A 3x enlargement of this image centered on M108 appears to the right.

This nearly edge-on spiral galaxy was discovered by P. Méchain in 1781. According to Stoyan et al. (2010), the distance of M108 is 46.0 million light years and its diameter is 100,000 light years.

For more information, see the Messier Catalog as well as specific entries for M108 in Wikipedia and SEDS.

Messier's Description of M108

Méchain in his letter to Bernoulli, May 6, 1783)
`Page 265 No. 97 [M97]. A nebula near Beta in the Great Bear. Mr. Messier mentions, when indicating its position, two others, which I also have discovered and of which one is close to this one [M108], the other is situated close to Gamma in the Great Bear [M109], but I could not yet determine their positions.' (from the description of M97)

`Nebula near [M97 and Beta UMa], [position] yet to be determined.'

Messier added a position by hand which Owen Gingerich identified in 1953 as NGC 3556, and is now called M108)

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